Re: Side effects of having NFSv4 mounted over udp

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Dec 14, 2010 at 08:35:14AM +0100, DENIEL Philippe wrote:
> Hi
> >The Linux server allows it, but I've been considering that a
> >(low-priority) bug, so it wouldn't be safe to assume it will continue
> >working.
> I am mostly thinking at the client side using as well udp and tcp.
> Would the "NFSv4 client over UDP" behaves differently then the same
> client over TCP ?
> 
> >That aside, if you have a perfect network,
> I can trust my network. It's not a WAN, it's located into a very
> massive cluster (it's kind of "internal LAN"). It's a very high
> throughput network (IB based) so I believe there are less "hardware
> based reason" to loose packets.
> 
> >NFSv4.0 at least will
> >probably work.
> OK.
> >(Not 4.1 since backchannel setup will fail?)
> What is erroneous in using UDP for NFSv4.1 backchannels ?

I assumed it would require some stronger notion of a "connection" than
UDP could provide.  But maybe it could be made to work somehow.

> >Are you really sure that you can't make tcp scale to thousands of
> >clients?
> I am a bit afraid of a "No more file descriptors" effect. If I have
> one TCP socket per client and thousands of clients, I have less
> remaining fds for other purposes. Another point : UDP is a "cheap"
> protocol. I can have bunches of clients without overloading the
> server (a new client will almost cost nothing to the server, just
> the cost of a new clientid negotiation) .

Is the tcp state all that much more?

> I was wondering if it
> could be reliable to use it for NFSv4 inside a large cluster.

Well, it'd require some spec changes in any case.

--b.